Dr Melvin Vopson and Dr Michal Belusky, from the Applied Materials Laboratory at the University of Portsmouth, UK, in collaboration with Dr John Naylor from the Kurt J. Lesker Company, recently demonstrated the successful deposition of flexible, magnetic nano thin films.
The ability to fabricate flexible nano-thin films is of great interest because of the increased demand for flexible technologies, a paradigm shift in high-tech and consumer electronics, already making significant technological and commercial impact by enabling the emergence of flexible photovoltaics, flexible electronics, flexible smart textiles and flexible displays. Flexible thin films are typically achieved by coating a given material onto a flexible substrate, via a chemical vapour deposition (CVD) process, where the coating ingredients are mostly organic materials and chemicals. Coating flexible thin films from inorganic materials such as metals, functional alloys, heterostructures, semiconductors, oxides and ceramics via solid state DC / RF plasma sputtering is less known, and it is unclear how the flexible substrate affects their properties. This project demonstrated the successful production of flexible magnetic thin films with excellent adhesion and mechanical robustness. Remarkably, the films maintained their structure, integrity and physical properties at any curvature bending applied to the flexible samples [see fig. 1].
It was also determined that the magnetic properties of the flexible films are identical to the films coated onto solid substrates, indicating that inorganic flexible thin films could be successfully fabricated via magnetron plasma sputtering. The tests were undertaken for NiFe, Co and Fe thin films with thickness ranging from 5nm to 100 nm. However, an interesting increase in the magnetic coercive field for flexible thin films thinner than 60 nm was observed. This was linked to the induced magnetic anisotropy by the surface roughness of the flexible substrates, resulting in a significant increase in the magnetic coercive field. A linear relationship between substrate roughness and the value of the magnetic coercive field has been universally observed for all the samples investigated. These experimental findings were reported at the JEMS conference in Sweden (2019) and published in Physica B and JMMM journals [1-3].
The films were grown using a Kurt J. Lesker LabLine SPUTTER 5 magnetron plasma sputtering [fig.2] equipped with four indexed substrate holders that can be independently rotated into the deposition position above one of the 5 magnetron Torus 2 sputtering targets. The base pressure was 5x10-7 Torr. An RF plasma cleaning procedure was applied to all substrates using 50W RF power, 10 mTorr Argon gas process pressure and 2 minutes duration per substrate. The temperature of the substrates was monitored and kept constant at 27°C during the deposition processes, which was performed at 3 mTorr Argon process pressure and 60 W DC power.
References
[1] M. Vopson, J. Naylor, T. Saengow, E.G. Rogers, S. Lepadatu, Y. Fetisov, Development of flexible Ni80Fe20 magnetic nano-thin films, Physica B: Condensed Matter, 525, 12-15 (2017).
[2] M. Belusky, S. Lepadatu, J. Naylor, M. Vopson, Evidence of substrate roughness surface induced magnetic anisotropy in NiFe flexible thin films, Journal of Magnetism and Magnetic Materials, 478, 77-83 (2019).
[3] M. Belusky, S. Lepadatu, J. Naylor, M. Vopson, Study of roughness effect in Fe and Co thin films prepared by plasma magnetron sputtering, Physica B: Condensed Matter 574, 411666 (2019).